U.S. Pat. No. 3,949,722 discloses an ignition system which has an overvoltage protection for the ignition coil. However, in the system of this patent, the criterion for overvoltage is the maximum allowable voltage across the primary winding of the ignition coil. However, it has now been found that limiting the voltage across the primary winding of the ignition coil is not sufficient to prevent overvoltages across the secondary winding under certain conditions. For example, if there is a break in the line between the secondary of the ignition coil and the spark plug, the capacitance in the secondary circuit of the ignition coil decreases to such an extent that excess voltages can result in burning up insulation.